The sea provides passageway to 45,000 merchant ships worldwide and over 90 percent of global trade.' Each year, 2.2 billion passengers, 40 percent of international tourists, and 44 million tons of freight travel by air. The global economic impact of air transport in 2007 was estimated to be $3.5 trillion, or 7.5 percent of global GDP.2 Additionally, the economic worth of the commu- nications, imagery, and positioning data gained from satellites in space was $257 billion in 2008, and each day, financial traders in New York City transfer more than $4 trillion, or approximately 25 percent of annual U.S. GDP, via the Internet.' As the 2010 U.S. Department of Defense's QuadrennialDefense Review Report states, "Global security and prosperity are contingent on the free flow of goods shipped by air or sea, as well as information transmitted under the ocean or through space."' Access to the global commons enables these flows, in turn promoting both international stability and prosperity.
Indeed, global commerce, travel, and information have greatly contributed to the growing wealth of nations and to the stability of the post-Cold War international system. The world's seas, air, space, and-more recently- cyberspace also play critical roles in states' national defense and their ability to conduct military operations worldwide. The United States relies on free- dom to operate in the commons in order to protect the U.S. homeland and its vital national interests. Yet as the global commons grows, the number of emerging trends that threaten this freedom of action also increases.